1. Field of the Invention
The present invention relates to die ejector chucks and die-pick up collets for removing a die from a sawn wafer mounted on a flexible adhesive membrane. More particularly, the present invention relates to a chuck apparatus for peeling the flexible membrane from beneath the edges of a selected die on a wafer prior to picking up the die with a die collet.
2. Description of the Prior Art
Heretofore, manufacturers of semiconductor devices have employed several techniques to separate individual die (chips) from each other after being manufactured in wafer form. The wafers have been diamond scribed and broken to separate them one from another, but this presents problems of having to reorient the separated die for pick-up and also has caused damage when the individual die or chips rub against each other and damage the active surfaces.
It has been found that the above problems could be eliminated if the wafers were saw cut with precision diamond saws so as to isolate individual die by the width of the saw and leave the die mounted on an adhesive surface. When the adhesive holding force is small or negligible, it is possible to lift or pull the selected die off of the adhesive membrane carrier without damaging the die. As the chips size have increased in area during the manufacture of very large scale integrated (VLSI), the adhesive beneath the die increases in holding force resulting in the requirement of much higher pick-up forces. Die eject pins have been incorporated into die chucks and have been employed on the back side of the adhesive membrane to push the adhesive membrane opposite the pre-selected die while the die collet is contacting and pulling on the selected die on the opposite side. This reduces the amount of pull force required by the die collet to separate a die from the adhesive carrier. Such prior art die chucks are shown and described in co-pending application Ser. No. 855,099 filed Apr. 22 1986 for "Apparatus For and Methods of Die Bonding" U.S. Pat. No. 4,797,994 which is assigned to the same assignee as the present invention.
Die sizes have increased for large scale integrated circuits to the point that the adhesive force holding the die cannot consistently be overcome without causing some damage to the die being picked up. If the die eject force of the die eject pin becomes too great, the die collet can damage the active surface of the die. If the die eject force of the die eject pin is reduced to avoid the pinching force, the die has a tendency to pivot at the edge of the die where there is the greatest adhesive force and cannot be removed by the vacuum operated die collet because the die tilts and the vacuum pulling force of the die collet is reduced or lost.
It would be desirable to provide a die eject chuck which overcomes the above-mentioned problems and presents a selected die for pick-up using a convention die collet with a force so reduced as not to damage the active surface of the die.